U.S. Pat. No. 3,553,032 discloses the method of making a fuel cell electrode comprising a porous bonded matrix of water repellent polymer particles having a thin coating of silver and particles of an electrically conductive material interspersed therein and adhering to said matrix which comprises forming a mixture of a water repellent polymer, particles of an electrically conductive material, and particles of silver carbonate, molding said mixture under pressure to form a coherent structure and heating the resulting coherent structure at a temperature above the decomposition temperature of said silver carbonate but below the softening point of said polymer to thereby form silver and liberate carbon dioxide gas which diffuses through said structure to render it substantially porous. U.S. Pat. No. 3,553,032 fails to teach the use of an alternative binder to cold sinterable fluorinated resins such as polytetrafluoroethylene, fluorinated ethylene-propylene, chlorotrifluoroethylenes, and polyvinylidine fluorides.
GB 2,316,801A discloses an electrocatalytic gas diffusion electrode for fuel cells comprised of: an anisotropic gas diffusion layer that is made of a porous carbon matrix through which carbon particles and poly(vinylidene fluoride) are distributed such that the matrix is homogeneously porous in a direction lateral to gas flow and asymmetrically porous to gases in the direction of gas flow, the porosity of said gas diffusion layer decreasing in the direction of gas flow, said gas diffusion layer having a thickness between about 50 μm and about 300 μm, and a catalytic layer that is made of a coagulated “ink” suspension containing catalytic carbon particles and a thermoplastic polymer, the catalytic layer covering the small pore surface of said gas diffusion layer, said catalytic layer having a thickness between about 7 μm and about 50 μm and a metal catalyst loading between about 0.1 mg/cm2 and about 0.5 mg/cm2.
EP 1 930 974A1 discloses 1. A method of producing a reversible solid oxide cell, comprising the steps of: tape casting an anode support layer on a support (1); tape casting an anode layer on a support (2); tape casting an electrolyte layer on a support (3); and either laminating said anode layer on top of said anode support layer; removing said support (2) from said anode layer; laminating said electrolyte layer on top of said anode layer; and sintering the multilayer structure; or laminating said anode layer on top of said electrolyte layer; removing said support (2) from said anode layer; laminating said anode support layer on top of said anode layer; and sintering the multilayer structure.
WO 03/082958A1 discloses a membrane electrode assembly, comprising: an anode; a cathode; and a proton exchange membrane positioned between the anode and cathode, wherein at least one of the anode, the cathode, and the proton exchange membrane comprises a sulfonate copolymer having the following chemical structure:
wherein; n/n+m ranges from about 0.001 to about 1; Y may be —S—, S(O), S(O)2, C(O), or P(O) (C6H5), and combination thereof; and Z may be a direct carbon-carbon single bond, C(CH3)2, C(CF3)2, C(CF3)(C6H5), C(O), S(O)2, or P(O) (C6H5).
U.S. Pat. No. 7,301,002B1 discloses a sulfonated polyphenylene polymer, derived by controllably sulfonating a polyphenylene polymer with a sulfonating agent, the sulfonated polyphenylene polymer having repeat units of the following structure 1:
in which R1, R2 and R3 are the same or different, wherein each R1, R2 and R3 is H or an unsubstituted or inertly-substituted aromatic moiety; Ar1 and Ar2 are the same or different, wherein each Ar1 and Ar2 is an unsubstituted aromatic moiety or inertly-substituted aromatic moiety; wherein a pendant side chain of a sulfonyl group attaches to a carbon atom; wherein from one to six sulfonyl groups are attached per repeat unit; wherein n≦0.2; and wherein any combination of R1, R2 and R3 and Ar1 and Ar2 comprises a sub-combination selected from the group consisting of; a) R1 is different than R2, b) R1 is different than R3, c) R2 is different than R3, d) Ar1 is different than Ar2, and e) R1.═R2.═R3═Ar1.═Ar2.
In 2004 M. Cifrain et al. in Journal of Power Sources, volume 127, pages 234-242, reported that Alkaline fuel cells (AFCs), although known to have a high efficiency, were considered to be only useful for space applications due to their high price, their low lifetime and their high carbon dioxide sensitivity and that AFCs can be built low-cost and CO2 reconcilable with sufficient lifetimes for vehicles and backup systems. They reported that key is a liquid circulating electrolyte which avoids many problems that membrane systems have, like the water and the heat management. Furthermore, M. Cifrain et al. reported that a standard AFC-electrode consists of several PTFE-bonded carbon black layers sometimes also containing other hydrophobic materials like paraffin wax or other plastics like polyethylene (PE) or polysulfone (PSU), that other additives are graphite (for increasing the electrical conductivity) and pore-formers (like sugar) and that sometimes porous PTFE foils are pressed onto the gas side, the electrodes being produced by rolling, pressing and sintering procedures.
F. Bidault et al. in 2009 in Journal of Power Sources, volume 187, pages 39-48, reviewed gas diffusion cathodes for alkaline fuel cells and reported that the overall performance and stability is dominated by the behaviour of the cathode, leading to a focus of research effort on cathode development. They further stated that the performance and durability of the gas diffusion electrode is very much dependent upon the way in which the layer structures are fabricated from carbon and polytetrafluoroethylene (PTFE) and that the choice and treatment of the carbon support is of primary importance for the final catalytic activity. They reported that, in general, AFC electrodes consist of several PTFE-bonded carbon black layers, which fulfil different functions, that modern electrodes tend to use high surface area carbon supported catalysts and PTFE to obtain the necessary three phase boundary (TPB) and that pressing, rolling, screen-printing and spraying methods are used in the production of AFC electrodes.
V. Neburchilov et al. in 2010 in Journal of Power Sources, volume 195, pages 1271-1291, reviewed the compositions, designs and methods of fabrication of air cathodes for alkali zinc-air fuel cells and reported that the more promising compositions for air electrodes are based on individual oxides, or mixtures of such, with the spinel, perovskite, or pyrochlore structure; MnO2, Ag, Co3O4, La2O3, LaNiO3, NiCo2O4, LaMnO3, LaNiO3 etc, which provide the optimum balance of ORR activity and chemical stability in an alkali electrolyte. They further reported that sol-gel and reverse micelle methods supply the most uniform distribution of the catalyst on the carbon and the highest catalyst BET surface area and that the design of the air cathode, including types of carbon black, binding agents, current collectors, Teflon membranes, thermal treatment of the gas diffusion layer, and catalyst layers, has a strong effect on performance.
WO 99/45604A discloses a method for preparing an electrode film, said method comprising the steps of: (a) forming an electrode mixture comprising either an anodic material or cathode active material, a polymer and a carrier solvent; and (b) contacting the electrode mixture with a polymer non-solvent to extract at least a portion of the carrier solvent from the electrode mixture to form an electrode film, but no hydrophobic layer is disclosed.
U.S. Pat. No. 6,521,381 discloses method of making an electrode structure comprising the steps of: (a) providing a current collector sheet; (b) forming a mixture comprising proton conductive material and carbon particles; (c) applying the mixture onto the current collector sheet and forming a film from the mixture, the film having first and second surfaces with the first surface adhered to the sheet; and then (d) generating a flux of metal atoms and collecting the atoms on the second surface of the film to form dispersed metallic polycrystals on the second surface of the film, wherein the flux of metal atoms is generated by physical vapor deposition, the physical vapor deposition occurring in a manner which maintains physical characteristics of the metal atoms throughout generation and collection. However, hot press manufacturing techniques are disclosed and there is no mention of phase inversion or the use of coating techniques.
US 2002-0127474A discloses an electrochemical system comprising: an electrochemical cell including: (a) an anode; (b) a cathode, and (c) a selectively proton-conducting membrane disposed between, and being in communication with, said anode and said cathode, said membrane comprising: (a) a hydrophobic matrix polymer and (b) a hydrophilic non-ionic polymer, wherein said hydrophobic polymer and said hydrophilic polymer form together a selectively proton-conducting membrane. US 2002/0127474A1 exemplifies the use of phase inversion techniques to provide an asymmetric membrane that contains pores on one side which are selective to proton passage while at least partially rejecting other cations, anions, and some neutral molecules.
US 2004/0028875A1 discloses a method of making a product with a micro to nano sized structure using a mould having a corresponding structure at a mould surface in which a fluid containing a casting material is brought info contact with said mould surface characterised in that the fluid is subjected to a treatment to induce phase separation therein, in that the said casting material is at least partially solidified on the mould surface and in that the resulting product is released from the mould surface.
US 2009/0228836A1 discloses a process for making an electrode sheet for a lithium electrochemical cells comprising the steps of: a) admixing a polyether polymer or copolymer soluble in water, at least one lithium salt, at least one electrochemically active material, water and an organic solvent miscible with water in a water/organic solvent ratio of a maximum of 50% organic solvent by volume to form a water-based solution/suspension containing by weight at least 20% active electrode material, at least 5% of a polyether polymer or copolymer, and at least 1.5% lithium salt; b) coating the water-based solution/suspension in the form of an electrode thin film onto an electrode support; and c) drying the electrode thin film to obtain an electrode thin sheet having less than 1000 ppm of residual water. Coating is performed on a current collector and phase inversion is realised by drying to remove the solvent.
WO 2006/015482A discloses a process for preparing an ion-permeable web-reinforced separator membrane, comprising the steps of: providing a web (2A) and a suitable paste (5), guiding said web (2A) in a vertical position, equally coating both sides of said web with said paste to produce a paste coated web (2B), and applying a symmetrical surface pore formation step and a symmetrical coagulation step to said paste coated web to produce a web-reinforced separator membrane. WO 2008/015482A discloses the reinforcement of coatings by coating on a polymeric web. Applications in alkaline water electrolysis, Batteries (acid and alkaline). Fuel cells and combinations thereof, were envisaged.
Widespread use of fuel cells is inhibited by the high cost of gas diffusion electrodes with the necessary balance of properties to function efficiently long term in fuel cells, e.g. in alkaline fuel cells, size limitation due to the production techniques used and the inability of conventional manufacturing techniques to be adapted for use in continuous production lines.
There is therefore a need to develop a radically different approach to the manufacture of gas diffusion electrodes for fuel cells while retaining the balance of properties necessary for the efficient long term functioning in fuel cells.